Okay, we got a really important clinical question here of a 27-year-old man
who is brought to the emergency department with his family
because of abdominal pain, excessive urination, and drowsiness since the day before arriving.
He has had type 1 diabetes milletus for two years.
He ran out of insulin two days ago.
His vital signs at admission are a temperature of 36.8 degrees Celsius,
a blood pressure of 102/69, and a pulse of 121.
On physical examination, he is lethargic and his breathing is rapid and deep.
There is a mild generalized abdominal tenderness without rebound or guarding.
His serum glucose is 480. Arterial blood gas of this patient will most likely show which of the following?
Answer choice A: Increase pH, increase bicarbonate and normal pCo2;
Answer choice B: Increased pH, normal bicarbonate and decreased pCo2;
Answer choice C: Decreased pH, normal bicarbonate and increased pCo2;
Answer choice D: Decreased pH, decreased bicarbonate and increased anion gap; and
Answer choice E: Decreased pH, decreased bicarbonate and a normal anion gap
Now take a moment to come to your own conclusion of an answer choice before we go through it together.
Okay, this is a very important question and absolutely you're going to see it on USMLE step two.
This is bread and butter parts of internal medicine
and what many of you will be dealing with during your intern residency
and even during med school, it's that common.
So let's go through the question characteristics.
This is an internal medicine question and we can see the patient's coming again with really an endocrine problem.
A serum glucose of 480, okay, that's not normal.
Now, this is a two-step question.
First thing we have to do is determine diagnosis and then after that,
we have to determine what would the ABG look like in that diagnosis.
And of course, the stem is absolutely required because we need to be able to take different pieces of information
and bring them together to diagnose and then figure out the ABG. So let's first determine the diagnosis.
We're told this patient has type 1 diabetes milletus.
In the question stem, it is said that he ran out of insulin two days ago
so he has really an acute insulin decompensation since he ran out of it.
His body was using it and then suddenly, for two whole days, he's really running low on insulin.
In the question stem, it's also said that he has marked hyperglycemia- his serum glucose is 480.
The lack of insulin means that glucose cannot be drawn into the cells and this causes excess glucose in the blood.
This is important for another understanding that that actually causes more problems.
If you look, the kid's blood pressure is 102/69, he's hypotensive and that's caused by dehydration
because the excessive blood glucose causes excessive blood glucose to then be in the urine
which actually draws water out of the body to go into the urine so you actually get hypotension as a result of hyperglycemia.
Very important to understand that pathology or really hear that pathophysiology.
When your body doesn't have insulin and you can't draw glucose into cells,
your body has to use an alternative energy source, there's no way around it.
Really, what ends up happening is ketones are used by the body which actually will then cause acidosis.
You know he has the symptomatic signs of acidosis because, in the question stem, it said that he has abdominal tenderness.
That's caused from metabolic acidosis, very important to know this.
Also, he has an unusual breathing pattern that they highlighted.
They said his breathing is rapid and deep. This is very, very important.
That's called Kussmaul breathing or Kussmaul respirations.
That pattern of breathing, of breathing rapid, and breathing deep is very important to understand, we call it Kussmaul respirations.
That's how your body is actually compensating due to this metabolic acidosis
by breathing really fast and deep to try to breath off the CO2.
So what's the diagnosis here?
It's diabetic ketoacidosis.
He's diabetic, he ran out of insulin, he's got a really high blood glucose, we see there's signs of metabolic acidosis,
abdominal pain and we see that we can diagnose him with diabetic ketoacidosis or DKA,
something very common in the hospital and everyone's going to be treating it.
We now need to figure out, okay, the diagnosis is DKA.
Got it, but what's the pH look like?
What's the bicarb gonna look like?
What my ABG overall gonna be in a patient with DKA?
This DKA that we will very commonly see and it's what we also see in this question stem is diabetic ketoacidosis
and that's a metabolic acidosis with respiratory compensation
because we're doing Kussmaul breathing.
If it's acidosis, the pH has to be less than 7.35 so automatically, you can remove answer choices A and B
because those are clinical states of alkalosis, the pH being elevated.
So you can already get those two out of there.
We know with DKA, we have a metabolic acidosis so that means the bicarb's going to be low.
So then you can eliminate answer choice C, which said they would have normal bicarb.
This is something you just have to memorize and also understand.
Diabetic ketoacidosis is an anion gap. Metabolic acidosis, that's, you gotta just ingrain that into your brain.
They're gonna say it so commonly over your career.
An anion gap is present in patients that have DKA because they have excess acids.
An anion gap is calculated by taking your sodium, adding potassium,
and then subtracting the sum of the chloride and the bicarb and that measures the amount of anions
and the overall charge that needs to be there in the body's blood.
So when a patient has DKA, they have excess ketones running around that's going to eat up the bicarb
and you're going to have an acidotic state and you're going to have an anion gap.
So this is something you just tattoo it on your hand if you have to.
Diabetic ketoacidosis is an acidotic state, so low bicarb.
It's a metabolic acidosis so the body will have low bicarbonate and you're going to have a high anion gap.
So diabetic ketoacidosis is going to have a low pH, a low bicarb, and a high anion gap, so that's answer choice D.
When we were going through these answer choices, we get rid of A and B
because those were alkalotic states, which is not going to be seen in diabetic ketoacidosis.
We also get rid of answer choice C because that had a normal bicarb which in a metabolic acidosis, we're not going to have.
Then you are left with answer choice D and E and you can easily eliminate answer choice E
because that has a normal anion gap.
In a classic DKA picture, it's a metabolic acidosis anion gap. That's something you just have to memorize.
Let's go through some of the other understandings of DKA.
In this case, the person who had diabetic ketoacidosis ran out of insulin
so inadequate insulin is very common to understand as something that's going to cause DKA.
But remember, other things can cause DKA.
This is really important for USMLE.
I don't want you just thinking, "Oh, there's insulin, can't be DKA."
No, no, no, no, you can definitely get DKA in other settings.
So, inadequate insulin therapy is the most common way to get DKA
but also infection, and especially pneumonia, and urinary tract infections are the two most common precipitating factors
that can cause DKA. Underlying medical conditions: say, a person has a stroke or they have a heart attack.
That causes the release of counterregulatory hormones like cortisol, glucagon, growth hormone, and even catecholamines.
Other medical conditions can actually be associated with DKA.
Say, Cushing's, acromegaly, hyperthyroid, having a stroke, pancreatitis.
So don't just think low insulin from not taking it is going to cause DKA.
Having an infection, having a metabolic condition, or a medical condition can actually trigger you to go into DKA as a diabetic.
Even medications can precipitate the development of DKA.
If you were to give someone steroids, thiazides, sympathomimetics like dobutamine.
Give some cocaine, or if they take it or a second-generation antipsychotic.
All of these things can cause someone to go into DKA even if they were taking their normal insulin therapy.
Refer to the image you see here so we can talk about the different manifestations of diabetic ketoacidosis.
One of them is going to be hyperglycemia.
This is a very key diagnostic criteria and you will have polyuria, polydipsia, polyphagia, fatigue, and weight loss.
Very common in the setting of hyperglycemia.
About 10% of patients with DKA will actually have a serum glucose less than 250.
So we call that euglycemic DKA but rare.
But you can still rely on the clinical findings of elevated hyperglycemia to help you still diagnose.
Academia is something we're always going to see,
in which you have abdominal pain, nausea, vomiting, and Kussmaul respirations.
We're also going to have the ketones in the body and very classically,
people like to say that they will notice on a patient's breath, due to the acetone of the ketone, a fruity odor.
Very high-yield. Dehydration, as we earlier discussed,
the hyperglycemia in the blood drawing out the water can cause dehydration in the patient
and you can see dry mucous membranes, poor skin turgor, tachycardia, increased BUN or creatinine, very classic,
and other things we can see really in severe diabetic ketoacidosis,
which is going to be some hypothermia, stupor, and even coma.
When looking at the ABG of diabetic ketoacidosis, we're going to see an anion gap metabolic acidosis.
Memorize that. The anion gap, again, is due to the production of the keto acids
and those are going to be beta-hydroxybutyrate, acetone, and acetoacetate.
Looking at our other answer choices, let's just quickly diagnose those
to make sure we will really know how to read those ABG as well.
Answer choice A, that's going to be metabolic alkalosis.
Elevated bicarb, that's going to be metabolic, there's no respiratory component, elevated pH.
Answer choice B, that's going to be a respiratory alkalosis.
As we can see the pCO2 is low from breathing it out, normal bicarb, and obviously elevated pH being alkalosis.
Answer choice C, that's going to be our respiratory acidosis,
in which we have an elevated pCO2 and a decreased pH from probably not breathing out enough,
holding in the CO2 and getting acidotic.
Answer choice E is a normal anion gap metabolic acidosis
and that can actually be seen in different states.
Hyperalimentation, Addison's, renal tubular acidosis, diarrhea, acetazolamide use,
spironolactone use, and saline infusion.
Now he mnemonic for that is HARD-ASS which you can use to know the different causes
of normal anion gap metabolic acidosis.
Now let’s review some high-yield facts. Ketosis.
Image here to review some of these high-yield facts.
Ketosis is the switch up metabolism from glucose to fat.
Fatty acids are then turned into ketone bodies during metabolism.
The main ketones you need to memorize are acetoacetate and beta-hydroxybutyrate.
Very common to see these in the USMLE exam.
It's caused by a lack of glucose, causing the body to turn to fat for an energy, so.
Acidosis, the low pH is going to be in the tissue and the blood and they can be either metabolic or respiratory.
Metabolic due to overproduction of acids or lack of removal of them in the urine
or it can be respiratory due to lack of removal of CO2 from hypoventilation.
The causes of metabolic acidosis overly multifold.
You can see them there on the image.
The signs and symptoms are also multifold.
They can include nausea, vomiting, palpitations, etc.
It can absolutely be potentially life-threatening.
You can have cardiovascular and neurological complications and extreme acidosis or academia.
Hyperglycemia, obviously, that's high blood glucose.
The main cause of diabetes can be actually quite multifold and you can see it there in our image.
The main signs and symptoms that you have to absolutely memorize for hyperglycemia, now memorize these:
polyuria, polydipsia, polyphagia, and fatigue.
Of course, diabetic ketoacidosis includes the triad of hyperglycemia ketoses and acidosis
and it's a common complication seen in type 1 diabetes and it can be rapid and onset.
It can happen within 24 hours of not having insulin or having some type of precipitating medical dysfunction.
It can absolutely be potentially life-threatening and you have to remember the treatment of diabetic ketoacidosis
includes giving potassium, giving insulin, and giving IV fluids.